The present invention relates to a system for controlling a warp let-off motion of a loom during downtimes, that is, a system for controlling the rotational movement of a warp beam when the loom is not in a normal weaving operation but moved by inching or by hand in a forward or reverse direction.
Let-off motions of looms, especially of a fluid jet type which is operated at high speeds, are usually provided with stepless speed change devices to guarantee a uniform warp tension from full to empty warp beam. One example of such stepless speed change devices is disclosed in Japanese patent examined publication No. 45-37180.
In this stepless speed change device, rotational movement of an input shaft is converted to movement of link means, and then the movement of the link means is converted again to rotational movement of an output shaft by the aid of a one-way clutch disposed between the link means and the output shaft. Therefore, the output shaft is rotated only in one direction whether the input shaft is rotated in forward direction or reverse direction.
If a malfunction such as a mispick is found during weaving operation, a loom in trouble is stopped for mending. However, a mispick is usually detected at a beating step following a weft inserting step especially in high speed jet looms, and there is a delay in subsequent response due to a time lag of a control circuit and/or delay in braking action. For these reasons, it is usual that a loom actually stops at the next weft-inserting step. Therefore, in order to remove a wrongly-inserted weft, it is necessary to rotate the loom in the reverse direction. In this case, the reverse rotation of the loom causes a reverae rotation of a woven fabric take-up motion because the take-up motion is connected with a driving shaft of the loom by a gear train. At the same time the reverse rotation of the loom causes a warp let-off motion to rotate in a forward direction because the let-off motion has a stepless speed change device of the above mentioned type. By these movements of the take-up motion and the let-off motion, the cloth fell is moved out of position, so that it is necessary to set the cloth fell in position again to restart the loom. Such a setting operation is necessary for preventing an undesired mark which is formed in the fabric at the position of the cloth fell when the weaving operation is restarted. However, this setting operation requires skill, and accordingly there is a strong demand for an automatic mechanism for doing such a setting operation automatically.
To meet this problem, Japanese patent provisional publication No. 56-68140 discloses a warp let-off mechanism which is provided with means for reversing the direction of output shaft rotation of a stepless speed change device in accordance with the direction of the loom rotation. However, this mechanism utilizes a worm gear, so that it requires a force increased by one and a half times to obtain the reverse rotation. Accordingly the construction of the stepless speed change device must be made strong enough to endure such an increased force, with the result of an increase of the manufacturing cost.